25 wssm olympic arms ar 15 upper It fits a regular ar15 lower. This is a new old stock never fired upper and it has a 20" stainless ultra barrel. I have 200 new brass, dies, a few loaded rds and 1 magazine. i have to many calibers to reload another. i may be interested in a 10 mm pistol or 1911 style partial trade. text for quick response thanks